1. Field of the Invention
This is a novel process which produces 2-isocyanatoalkyl esters of organic carboxylic acids in high yields. This process is particularly useful in preparing 2-isocyanatoalkyl esters of alkenoic acids.
2. Prior Art
The 2-substituted-2-oxazolines form a known class of compounds. The literature is replete with information regarding methods of preparation and use of such compounds. See, for example, the following review articles: (a) Wiley et al., Chemical Reviews, Vol. 44, 447 (1949); (b) Seeliger et al., Angew. Chem. Internat. Edit., Vol. 5, 10 (1966); and (c) Frump, Chemical Reviews, Vol. 71, 5 (1971). See also the patents classified by the U.S. Patent and Trademark Office under 260/307F.
The 2-alkenyl-2-oxazolines are particularly useful compounds due to their difunctionality. Of these, the 2-vinyl- and 2-isopropenyl-2-oxazolines are perhaps the best known. Prior art methods of preparing 2-alkenyl-2-oxazolines normally utilize relatively expensive reagents in multistep processes and the product yields were normally low. See, for example, the processes described in the above review articles and refer to the following U.S. Pat. Nos.: 2,831,858; 2,968,657; 3,248,397; 3,466,308; 3,505,297; 3,523,123; 3,535,332; 3,661,922; 3,678,065; 3,839,350; Fr. Pat. No. 1,557,954 and Ger. Offen. No. 2,302,168.
Another process for preparing 2-alkenyl-2-oxazolines was described by Lalk et al. in a commonly-owned U.S. patent application Ser. No. 699,091 filed June 23, 1976 and entitled "Method for Preparing 2-Alkenyl-2-Oxazolines." The disclosure of Ser. No. 699,091 is incorporated herein by reference. The process described in Ser. No. 699,091 comprises the steps of:
(1) reacting by contacting an anhydrous or substantially anhydrous 2-alkyl-2-oxazoline with formaldehyde in a molar ratio of at least about 1.5 mole of 2-alkyl-2-oxazoline per mole of formaldehyde, thereby forming the 2-(.alpha.-hydroxymethylalkyl)-2-oxazoline,
(2) recovering the 2-(.alpha.-hydroxymethylalkyl)-2-oxazoline from the reaction product of step (1), and
(3) reacting by contacting the 2-(.alpha.-hydroxymethylalkyl)-2-oxazoline from step (2) with an alkali or alkaline earth metal hydroxide, thereby forming the 2-alkenyl-2-oxazoline.
The 2-alkenyl-2-oxazoline thus produced is normally recovered by distillation as an aqueous solution. Water is formed as a by-product of the process and normally codistills with the 2-alkenyl-2-oxazoline. This crude aqueous 2-alkenyl-2-oxazoline is surprisingly useful in the instant process; it can be added per se into the reaction process, but, we prefer to dilute it with sufficient water to give about a 20 mole percent solution of oxazoline in water, and we most prefer to dilute to about a 5-10 mole percent concentration.
The use of a crude aqueous 2-alkenyl-2-oxazoline as prepared by the above process or any aqueous solution of a 2-oxazoline in the preparation of 2-isocyanatoalkyl esters of organic carboxylic acids is in direct contrast to the teachings of British Pat. No. 1,252,099. In the British patent, a 2-oxazoline dissolved in a water-immiscible solvent was reacted with phosgene (also dissolved in a water-immiscible solvent) in the presence of an aqueous solution of a hydrochloric acid acceptor.